The present invention relates to a compressor for use in, for example, a Stirling cryogenerator for producing very low temperature.
A machine for producing very low temperature, such a Stirling cryogenerator, utilizes, as one of its main constitutional components, a cryocompressor having a reciprocal piston or pistons for compressing gas such as helium.
FIG. 4 shows a partial cross sectioned front view of an example of a conventional cryocompressor, which was developed by the present inventors, and FIG. 5 is a cross sectional side view of the same. In FIGS. 4 and 5, a reference numeral 1 depicts a motor, 2 a crank shaft to be driven by the motor 1, 3 a connecting rod having one end supported by an eccentric portion of the crank shaft 2 through a bearing 4, 5 a piston connected to the other end of the connecting rod 3 and reciprocating within a cylinder 6, 7 a piston ring mounted on the piston 5 for sealing a chamber above the piston within the cylinder 6, 8 bearings supported by a motor casing 9 for rotatably supporting the crank shaft 2 and 10 a crank case provided between the cylinder 6 and the casing 9, to an upper end of which a gas pipe 11 is connected. A reference numeral 12 depicts a compression chamber formed in the cylinder 6 and a buffer chamber 13 is formed in the crank case 10. The compression chamber 12 is isolated from the buffer chamber 13 by the piston ring 7. A reference numeral 14 depicts a connecting circuit for communicating the compression chamber 12 with the buffer chamber 13 directly, and 15 a check vale provided in the connecting circuit 14 for allowing gas flow only from the buffer chamber 13 to the compression chamber 12.
A purification chamber 16 is provided in the connecting circuit 14 on the buffer chamberside thereof, which is filled with a purifying agent such a as molecular sieve.
In the cryocompressor constructed as above, the piston 5 reciprocates within the cylinder 6 by a rotation of the crank shaft 2 driven by the motor 1 to compress and expand the compression chamber 12 repeatedly to thereby discharge and intake a working gas from and into the gas pipe connected to the compression chamber 12.
In a state where gas pressure, Pc in the compression chamber 12 is higher than gas pressure P.sub.B in the buffer chamber, gas leaks from the compression chamber 12 through an annular gap between the piston ring 7 and the cylinder 6 to the buffer chamber 13. When gas pressure Pc in the compression chamber 12 is becoming lower than gas pressure P.sub.B in the buffer chamber 13, gas is introduced from the buffer chamber 13 through the check valve 15 provided in the connecting circuit 14 to the compression chamber 12. Therefore, as shown in FIG. 6 showing a crank angle with an upper death point being 0.degree., gas pressure Pc in the compression chamber 12 becomes equal to or higher than gas pressure, P.sub.B in the buffer chamber 13 so that gas flows from the compression chamber 12 through the gap between the piston ring 7 and the cylinder 6 and through the connecting circuit 14 to the compression chamber 12. Thus, as shown in FIG. 6, loads on the bearing and the connecting rod are in one direction, respectively, and therefore the possibility of noise generation due to gaps unavoidably existing in the bearings and the connecting rod is considerably reduced as compared with usual compressors having no check valve.
The cryocompressor such as shown in FIGS. 4 and 6 in which the compression chamber is connected through the connecting circuit having the check valve to the buffer chamber, directly, pressure in the compression chamber is always higher than pressure i the buffer chamber and thus the direction of loads on the connecting rd and the bearing portions is fixed. However, as shown in FIG. 6, since a piston side pressure changes in a direction corresponding to the crank angle and a side load acting on the piston is changed in direction according to the crank angle of the connecting rod, shock noise may be produced in these portions. Further, since the piston ring slides along a wall of the cylinder with a high pressure difference, the life thereof is considerably shortened by severe abrasion.